Ultrasonic transducer drive circuit and ultrasonic image display apparatus

ABSTRACT

An ultrasonic transducer drive circuit for driving an ultrasonic transducer by outputting pulses including a positive pulse and a negative pulse to an output line is provided. The ultrasonic transducer includes a positive voltage supply circuit, a negative voltage supply circuit, a current-inflow-type ground clamp circuit configured to operate when voltage in the output line is positive voltage, and a current-outflow-type ground clamp circuit configured to operate when voltage in the output line is negative voltage, wherein the current-inflow-type ground clamp circuit is configured to enter an operation state at a time of generating the negative pulse in a state where the voltage in the output line is positive voltage, and the current-outflow-type ground clamp circuit is configured to enter an operation state at a time of generating the positive pulse in a state where the voltage in the output line is negative voltage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application No.2011-109442 filed May 16, 2011, which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to an ultrasonic transducer drive circuitand an ultrasonic image display apparatus.

An ultrasonic transducer drive circuit is a circuit for driving anultrasonic transducer by outputting pulses made by a positive voltagepulse and a negative voltage pulse to an output line of the ultrasonictransducer. As such an ultrasonic transducer drive circuit, for example,Japanese Unexamined Patent Application Publication No. 2009-101072discloses a circuit having a positive voltage supply circuit forsupplying positive voltage to the output line and a negative voltagesupply circuit for supplying negative voltage to the output line. In theultrasonic transducer drive circuit, when a negative voltage pulse isgenerated in a state where the voltage in the output line is positivevoltage, the negative voltage supply circuit is operated and, togenerate a positive voltage pulse in a state where the voltage in theoutput line is negative voltage, the positive voltage supply circuit isoperated.

When the negative voltage supply circuit is operated at the time ofgenerating the negative voltage pulse in a state where the voltage inthe output line is positive voltage, current flows in the negativevoltage supply circuit for predetermined time and power is consumed.When the positive voltage supply circuit is operated at the time ofgenerating the positive voltage pulse in a state where the voltage inthe output line is negative voltage, current flows in the positivevoltage supply circuit for predetermined time and power is consumed.Therefore, suppression of power consumption in the positive voltagesupply circuit and the negative voltage supply circuit is an issue.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, an ultrasonic transducer drive circuit for driving anultrasonic transducer by outputting pulses made of a positive pulse anda negative pulse to an output line to the ultrasonic transducer isprovided. The ultrasonic transducer drive circuit includes a positivevoltage supply circuit for supplying positive voltage to the outputline, a negative voltage supply circuit for supplying negative voltageto the output line, a current-inflow-type ground clamp circuit whichoperates when voltage in the output line is positive voltage, andchanges the voltage in the output line to ground voltage, and acurrent-outflow-type ground clamp circuit which operates when voltage inthe output line is negative voltage, and changes the voltage in theoutput line to ground voltage. The current-inflow-type ground clampcircuit enters an operation state when the negative pulse is generatedin a state where the voltage in the output line is positive voltage, andthe current-outflow-type ground clamp circuit enters an operation statewhen the positive pulse is generated in a state where the voltage in theoutput line is negative voltage.

Accordingly, at the time of generating a negative pulse in a state wherethe voltage in the output line is positive voltage, the currentinflow-type ground clamp circuit operates in place of the negativevoltage supply circuit. At the time of generating a positive pulse in astate where the voltage in the output line is negative voltage, thecurrent-outflow-type ground clamp circuit operates in place of thepositive voltage supply circuit. Therefore, power consumption in thepositive voltage supply circuit and the negative voltage supply circuitcan be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of an embodiment of anultrasonic image display apparatus.

FIG. 2 is a block diagram showing a transmitting/receiving unit in theultrasonic image display apparatus illustrated in FIG. 1.

FIG. 3 is a circuit diagram showing an ultrasonic transducer drivecircuit in the ultrasonic image display apparatus illustrated in FIG. 1.

FIG. 4 is a diagram for explaining the operation of the ultrasonictransducer drive circuit shown in FIG. 3.

FIG. 5 is a diagram for explaining output current and power consumptionfrom time t1 to time t2.

FIG. 6 is a diagram for explaining output current and power consumptionfrom time t3 to time t4.

FIG. 7 is a diagram for explaining output current and power consumptionfrom time t4 to time t5.

FIG. 8 is a diagram for explaining output current and power consumptionfrom time t6 to time t7.

FIG. 9 is a diagram for explaining output current and power consumptionfrom time t7 to time t8.

FIG. 10 is a diagram for explaining the operation of a conventionalultrasonic transducer drive circuit.

FIG. 11 is a diagram for explaining output current and power consumptionfrom time t3 to time t4 in the conventional ultrasonic transducer drivecircuit.

FIG. 12 is a diagram for explaining output current and power consumptionfrom time t6 to time t7 in the conventional ultrasonic transducer drivecircuit.

FIG. 13 is a diagram for explaining the operation of an ultrasonictransducer drive circuit in a first modification of the firstembodiment.

FIG. 14 is a circuit diagram showing an ultrasonic transducer drivecircuit in a second modification of the first embodiment.

FIG. 15 is a diagram showing the configuration of a feedback unitillustrated in FIG. 14.

FIG. 16 is a diagram for explaining the operation of the ultrasonictransducer drive circuit in the second modification of the firstembodiment.

FIG. 17 is a diagram for explaining the operation of an ultrasonictransducer drive circuit in a second embodiment.

FIG. 18 is a diagram for explaining the flow of current from time t3 totime t4 in the ultrasonic transducer drive circuit of the secondembodiment.

FIG. 19 is a diagram for explaining the flow of current from time t6 totime t7 in the ultrasonic transducer drive circuit of the secondembodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail below with reference to thedrawings.

First Embodiment

First, a first embodiment will be described with reference to FIGS. 1 to9. As illustrated in FIG. 1, an ultrasonic image display apparatus 100has an ultrasonic probe 101, a transmitting/receiving unit 102, an echodata processing unit 103, a display control unit 104, a display unit105, an operation unit 106, and a control unit 107.

The ultrasonic probe 101 is provided with a plurality of ultrasonictransducers 101 a that transmit/receive ultrasonic waves.

The transmitting/receiving unit 102 has a transmitting unit 1021 and areceiving unit 1022 as illustrated in FIG. 2. The transmitting unit 1021supplies an electric signal for transmitting ultrasonic waves under apredetermined scan condition to the ultrasonic probe 101 on the basis ofa control signal from the control unit 107. The transmitting unit 1021has an ultrasonic transducer drive circuit 1 (not shown in FIG. 2, referto FIG. 3) which supplies an electric signal for transmitting ultrasonicwaves by driving the ultrasonic transducers 101 a. The ultrasonictransducer drive circuit 1 will be described later.

The receiving unit 1022 performs signal processes such as A/D conversionand phasing and adding process on an echo signal received by theultrasonic probe 101 and outputs obtained echo data to the echo dataprocessing unit 103.

The echo data processing unit 103 performs a process for generating anultrasonic image on the echo data supplied from thetransmitting/receiving unit 102. For example, the echo data processingunit 103 performs B-mode processes such as logarithmic compressionprocess and envelope detecting process, Doppler processes such asorthogonal detecting process and filter process, and the like.

The display control unit 104 scan-converts the data obtained by the echodata processing unit 103 by a scan converter to generate ultrasonicimage data. The display control unit 104 displays an ultrasonic imagebased on the ultrasonic image data on the display unit 105.

The display unit 105 is an LCD (Liquid Crystal Display), a CRT (CathodeRay Tube), or the like. The operation unit 106 includes a keyboard and apointing device (not shown) for entering an instruction and informationby an operator.

The control unit 107 has a CPU (Central Processing Unit). The controlunit 107 reads a control program stored in a not-shown storage andexecutes functions in the units in the ultrasonic image displayapparatus 100.

Next, the ultrasonic transducer drive circuit 1 will be described withreference to FIG. 3. The ultrasonic transducer drive circuit 1 isprovided for each ultrasonic transducer 101 a (only one is shown in FIG.3). The ultrasonic transducer driver circuit 1 outputs an electricsignal for driving the ultrasonic transducer 101 a to an output line Oconnected to the ultrasonic transducer 101 a. In the embodiment, theelectric signal is explained as voltage pulses made of a positivevoltage pulse and a negative voltage pulse.

The ultrasonic transducer drive circuit 1 has a positive voltage supplycircuit 2, a negative voltage supply circuit 3, a current-inflow-typeground clamp circuit 4, and a current-outflow-type ground clamp circuit5. The positive voltage supply circuit 2, the negative voltage supplycircuit 3, the current-inflow-type ground clamp circuit 4, and thecurrent-outflow-type ground clamp circuit 5 are connected to the outputline O.

The ultrasonic transducer 101 a is equivalent to a circuit in which acapacitor and a resistor are connected in parallel.

The positive voltage supply circuit 2 is a circuit for supplyingpositive voltage to the output line O on the basis of a positive powersupply voltage +HV and has a first transistor Tr1 and a first diode D1provided between the first transistor Tr1 and the output line O. Thefirst diode D1 is provided in a direction of passing current from thefirst transistor Tr1 to the output line O.

The first transistor Tr1 is a p-channel-type MOSFET (Metal-OxideSemiconductor Field-Effect Transistor). In the first transistor Tr1, apower source for supplying the positive voltage +HV is connected to thesource side, and the first diode D1 and the output line O are connectedto the drain side. To the gate of the first transistor Tr1, a firstdriver circuit 6 outputting a drive signal to turn on/off the firsttransistor Tr1 is connected. The positive voltage supply circuit 2enters an operation state when the first transistor Tr1 is in an onstate and supplies the positive voltage to the output line O.

The positive voltage supply circuit 2 is an example of an embodiment ofthe positive voltage supply circuit. The first transistor Tr1 is anexample of an embodiment of the first transistor. Further, the firstdriver circuit 6 is an example of an embodiment of the first drivercircuit.

The negative voltage supply circuit 3 is a circuit for supplying thenegative voltage to the output line O on the basis of a negative voltage−HV and has a second transistor Tr2 and a second diode D2 providedbetween the second transistor Tr2 and the output line O. The seconddiode D2 is provided in a direction of passing current from the outputline O to the second transistor Tr2.

The second transistor Tr2 is an n-channel-type MOSFET. In the secondtransistor Tr2, a power source for supplying the negative voltage −HV isconnected to the source side, and the second diode D2 and the outputline O are connected to the drain side. To the gate of the secondtransistor Tr2, a second driver circuit 7 outputting a drive signal toturn on/off the second transistor Tr2 is connected. The negative voltagesupply circuit 3 enters an operation state when the second transistorTr2 is in an on state and supplies the negative voltage to the outputline O.

The negative voltage supply circuit 3 is an example of an embodiment ofthe negative voltage supply circuit. The second transistor Tr2 is anexample of an embodiment of the second transistor. Further, the seconddriver circuit 7 is an example of an embodiment of the second drivercircuit.

The current-inflow-type ground clamp circuit 4 has a third transistorTr3 and a third diode D3 provided between the third transistor Tr3 andthe output line O. The third diode D3 is provided in a direction ofpassing current from the output line O to the third transistor Tr3. Thecurrent-inflow-type ground clamp circuit 4 is a circuit which enters anoperation state when the third transistor Tr3 is in an on state and towhich current flows in from the output line O, and is a circuit forchanging the positive voltage in the output line O to the groundvoltage.

The third transistor Tr3 is an n-channel-type MOSFET. In the thirdtransistor Tr3, the third diode D3 and the output line O are connectedto the drain side, and the source side is connected to the ground. Tothe gate of the third transistor Tr3, a third driver circuit 8outputting a drive signal to turn on/off the third transistor Tr3 isconnected.

The current-inflow-type ground clamp circuit 4 is an example of anembodiment of the current-inflow-type ground clamp circuit. The thirdtransistor Tr3 is an example of an embodiment of the third transistor.Further, the third driver circuit 8 is an example of an embodiment ofthe third driver circuit.

The current-outflow-type ground clamp circuit 5 has a fourth transistorTr4 and a fourth diode D4 provided between the fourth transistor Tr4 andthe output line O. The fourth diode D4 is provided in a direction ofpassing current from the fourth transistor Tr4 to the output line O. Thecurrent-outflow-type ground clamp circuit 5 is a circuit which enters anoperation state when the fourth transistor Tr4 is in an on state andcurrent flows out to the output line O, and is a circuit for changingthe negative voltage in the output line O to the ground voltage.

The fourth transistor Tr4 is a p-channel-type MOSFET. In the fourthtransistor Tr4, the fourth diode D4 and the output line O are connectedto the drain side, and the source side is connected to the ground. Tothe gate of the fourth transistor Tr4, a fourth driver circuit 9outputting a drive signal to turn on/off the fourth transistor Tr4 isconnected.

The current-outflow-type ground clamp circuit 5 is an example of anembodiment of the current-outflow-type ground clamp circuit. The fourthtransistor Tr4 is an example of an embodiment of the fourth transistor.Further, the fourth driver circuit 9 is an example of an embodiment ofthe driver circuit.

The operation of the ultrasonic transducer drive circuit 1 will now bedescribed with reference to FIG. 4. First, at time t1, the firsttransistor Tr1 changes from the off state to the on state, and the thirdtransistor Tr3 changes from the on state to the off state. At this time,the second transistor Tr2 remains in the off state, and the fourthtransistor Tr4 remains in the on state.

When the first transistor Tr1 changes to the on state, output voltage Voin the output line O rises from ground voltage Vg. At time t2 afterlapse of predetermined time from the time t1, the output voltage Vorises to positive voltage +V and, after that, is stabilized at thepositive voltage +V.

Next, at time t3 after lapse of predetermined time from the time t2, thefirst transistor Tr1 changes from the on state to the off state, and thethird transistor Tr3 changes from the off state to the on state. At timet3, the fourth transistor Tr4 changes from the on state to the offstate.

When the third transistor Tr3 changes to the on state at time t3, theoutput voltage Vo starts decreasing from the positive voltage +V. Attime t4 as a timing when the output voltage Vo changes to the groundvoltage Vg, the second transistor Tr2 changes from the off state to theon state. Consequently, the output voltage Vo becomes negative andbecomes negative voltage −V at time t5.

The time t4 as a timing when the second transistor Tr2 changes from theoff state to the on state is time after lapse of predetermined delaytime dt since the third transistor Tr3 changes from the off state to theon state. As the delay time dt, time required for the voltage in theoutput line to become the ground voltage Vg is preset.

The time t3 corresponds to time when a negative pulse is generated in astate where the voltage in the output line O is positive voltage.

The output voltage Vo becomes the negative voltage −V at time t5 and isstabilized. At time t6 after lapse of predetermined time since the timet5, the second transistor Tr2 changes from the on state to the offstate, and the fourth transistor Tr4 changes from the off state to theon state. At time t6, the third transistor Tr3 changes from the on stateto the off state.

By the change of the fourth transistor Tr4 to the on state at the timet6, the output voltage Vo starts rising from the negative voltage −V. Attime t7 as a timing when the output voltage Vo becomes the groundvoltage Vg, the first transistor Tr1 changes from the off state to theon state. As a result, the output voltage Vo becomes positive andbecomes again positive voltage +V at time t8.

Time t7 as a timing when the first transistor Tr1 changes from the offstate to the on state is time after lapse of predetermined delay time dtsince the fourth transistor Tr4 changed from the off state to the onstate. As the delay time dt, time required for the voltage in the outputline O to become the ground voltage Vg is preset.

The time t6 corresponds to time when a positive pulse is generated in astate where the voltage in the output line O is negative voltage.

At time t9 after lapse of predetermined time from the time t8, the firsttransistor Tr1 changes again from the on state to the off state, and thethird transistor Tr3 changes from the off state to the on state. At thetime t9, the fourth transistor Tr4 changes from the on state to the offstate.

The ultrasonic transducer drive circuit 1 repeats the above-describedoperation, thereby outputting pulses made of a positive pulse and anegative pulse to the output line O so that the ultrasonic transducers101 a drive. The pulse is a voltage pulse, the positive pulse ispositive voltage pulse, and the negative pulse is negative voltagepulse.

Consumption of output current Io in the output line O and power W willbe described with reference to FIGS. 5 to 9. It is assumed that theoutput current Io is current flowing in a part on the ultrasonictransducer 101 a side more than the part in which thecurrent-inflow-type ground clamp circuit 4 is connected and the part inwhich the current-outflow-type ground clamp circuit 5 is connected inthe output line O.

FIGS. 5 to 9, the first transistor Tr1 to the fourth transistor Tr4 aresimplified and shown as switches.

In a period from time t1 to time t2, as shown in FIG. 5, current i1flows in the positive voltage supply circuit 2, and current +I flows asthe output current Io. At this time, power W is consumed in the positivevoltage supply circuit 2 (refer to FIG. 4).

In a period from time t3 to time t4, as shown in FIG. 6, current i3flows in the current-inflow-type ground clamp circuit 4, and current −Iflows as the output current Io. At this time, since the secondtransistor Tr2 is in the off state, no current flows in the negativevoltage supply circuit 3, and no power is consumed in the negativevoltage supply circuit 3.

In a period from time t4 to time t5, as shown in FIG. 7, current i2flows in the negative voltage supply circuit 3, and the current −I flowsas the output current Io. At this time, the power W is consumed in thenegative voltage supply circuit 3.

In a period from time t6 to time t7, as shown in FIG. 8, current i4flows in the current-outflow-type ground clamp circuit 5, and thecurrent +I flows as the output current Io. At this time, since the firsttransistor Tr1 is in the off state, no current flows in the positivevoltage supply circuit 2, and no power is consumed in the positivevoltage supply circuit 2.

In a period from time t7 to time t8, as shown in FIG. 9, the current i1flows in the positive voltage supply circuit 2, and the current +I flowsas the output current Io. At this time, the power W is consumed in thepositive voltage supply circuit 2.

In a period from time t2 to time t3 and a period from time t5 to timet6, current flows in a resistance component in the ultrasonic transducer101 a, current flows in the positive voltage supply circuit 2 and thenegative voltage supply circuit 3 only by the amount of the current, andpower is consumed.

To explain the fact that power consumption is suppressed more than theconventional technique by the ultrasonic transducer drive circuit 1 ofthe embodiment, the operation of a conventional ultrasonic transducerdrive circuit will be described with reference to FIG. 10. Theconventional ultrasonic transducer drive circuit has the sameconfiguration as that of FIG. 3.

Only points different from the operation of the ultrasonic transducerdrive circuit 1 of the embodiment will be described. First, at time t1,operation is similar to that of the ultrasonic transducer drive circuit1 of the embodiment except that the transistor Tr4 changes from the onstate to the off state. The transistors Tr3 and Tr4 continue in the offstate since the time t1 and change to the on state at time t10 as thetiming of changing the output voltage Vo to the ground voltage Vg.

At time t3, the first transistor Tr1 changes from the on state to theoff state and the second transistor Tr2 changes from the off state tothe on state. At time t6, the second transistor Tr2 changes from the onstate to the off state, and the first transistor Tr1 changes from theoff state to the on state.

In FIG. 10, alternate long and two short dashes lines indicate theoperation in the ultrasonic transducer drive circuit 1 of theembodiment.

The output current Io and consumption of the power W in an output lineO′ in a conventional ultrasonic transducer drive circuit 1′ performingsuch operation will be described with reference to FIGS. 11 and 12,particularly, in comparison to the embodiments described herein. In aperiod from time t3 to time t4, as shown in FIG. 11, current i2 flows inthe negative voltage supply circuit 3, and the current −I flows as theoutput current Io. At this time, the power W is consumed in the negativevoltage supply circuit 3.

In the period from time t6 to time t7, as shown in FIG. 12, the currenti1 flows in the positive voltage supply circuit 2 and the current +Iflows as the output current Io. At this time, the power W is consumed inthe positive voltage supply circuit 2.

On the other hand, in the ultrasonic transducer drive circuit 1 of theembodiment, at time t3 as time when the negative pulse is generated in astate where the voltage in the output line O is positive voltage, thethird transistor Tr3 enters the on state. In the delay time dt from timet3 to time t4, the current-inflow-type ground clamp circuit 4 enters theoperation state in place of the negative voltage supply circuit 3. Thefourth transistor Tr4 enters the on state at time t6 when the positivepulse is generated in a state where the voltage in the output line O isnegative voltage. In the delay time dt from time t6 to time t7, thecurrent-outflow-type ground clamp circuit 4 operates in place of thepositive voltage supply circuit 2. Therefore, in the ultrasonictransducer drive circuit 1 of the embodiment, in the period from time t3to time t4 and the period from time t6 to time t7, no power is consumedin the positive voltage supply circuit 2 and the negative voltage supplycircuit 3 (the alternate long and short dashes line in FIG. 10), so thatthe power consumption in the positive voltage supply circuit 2 and thenegative voltage supply circuit 3 can be suppressed only by the amountmore than the conventional technique.

Next, modifications of the first embodiment will be described. First, afirst modification will be described with reference to FIG. 13. Thethird transistor Tr3 does not have to be in the on state to the time t6but may be in the on state until at least time t4, that is, until thepositive voltage in the output line O becomes the ground voltage Vg. Thefourth transistor Tr4 does not have to be in the on state till time t9but may be in the on state until at least time t7, that is, until thenegative voltage in the output line O becomes the ground voltage Vg.

The transistor Tr4 may change from the on state to the off state at thetime t1.

A second modification will now be described. In the second modification,the delay time dt is not preset but is determined on the basis of theoutput voltage Vo. Concretely, as shown in FIG. 14, the ultrasonictransducer drive circuit 1′ of the second modification has a feedbackunit 10. The input side of the feedback unit 10 is connected to theoutput line O. The output side of the feedback unit 10 is connected tothe first driver circuit 6 and the second driver circuit 7.

The feedback unit 10 is constructed by a window comparator Wi shown inFIG. 15. To the window comparator Wi, the output voltage Vo of theoutput line O is supplied. The window comparator Wi compares the outputvoltage Vo with a positive threshold voltage +Vth and a negativethreshold voltage −Vth and outputs a signal to the first driver circuit6 and the second driver circuit 7.

The range of the negative threshold voltage −Vth or higher and thepositive threshold voltage +Vth or lower includes the ground voltage Vg,and is an example of the embodiment of the voltage in the predeterminedrange.

The operation of the second modification will be described withreference to FIG. 16. Points different from the foregoing embodimentwith respect to the operations of the first transistor Tr1 and thesecond transistor Tr2 will be described. The operations of the thirdtransistor Tr3 and the fourth transistor Tr4 are the same as those ofthe foregoing embodiment, so that the description will not be repeated.

At time t3, the output voltage Vo starts decreasing from the positivevoltage +V. When the output voltage Vo becomes the positive thresholdvoltage +Vth at time t4′, the feedback unit 10 outputs a signal whichmakes the second transistor Tr2 enter the on state to the second drivercircuit 7. By the signal, the second transistor Tr2 is turned on. Asdescribed above, the output voltage Vo becomes close to the groundvoltage Vg from the positive voltage +V, the second transistor Tr2changes from the off state to the on state, so that the output voltageVo becomes negative voltage.

When the output voltage Vo starts rising from the negative voltage −V attime t6 and becomes the negative threshold voltage −Vth at time t7′, thefeedback unit 10 outputs a signal which makes the first transistor Tr1enter the on state to the first driver circuit 6. By the signal, thefirst transistor Tr1 is turned on. As described above, the outputvoltage Vo becomes close to the ground voltage Vg from the negativevoltage −V, the first transistor Tr1 changes from the off state to theon state, so that the output voltage Vo becomes positive voltage.

Also in the second modification, as the delay time dt, time from thetime t3 to time t4′ or time from time t6 to time t7′ is assured, and thepower consumption can be suppressed more than the conventionaltechnique.

Second Embodiment

Next, a second embodiment will be described. The ultrasonic transducerdrive circuit 1 of the second embodiment has the same configuration asthat of FIG. 4, and operations different from those of the firstembodiment will be described now.

In the ultrasonic transducer drive circuit 1 of the embodiment, as shownin FIG. 17, the second transistor Tr2 changes from the off state to theon state at time t3. At time t6, the first transistor Tr1 changes fromthe off state to the on state. That is, in the embodiment, there is nodelay time dt.

In the ultrasonic transducer drive circuit 1 of the embodiment,different from the first embodiment, when the third transistor Tr3changes from the off state to the on state, the second transistor Tr2changes from the off state to the on state. When the fourth transistorTr4 changes from the off state to the on state, the first transistor Tr1changes from the off state to the on state. Also in such an ultrasonictransducer drive circuit 1 of the embodiment, the power consumption canbe suppressed more than the conventional technique. The consumption ofthe power W will now be described with reference to FIGS. 18 and 19.

When the second transistor Tr2 and the third transistor Tr3 enter the onstate at time t3, as shown in FIG. 18, current i2′ flows in the negativevoltage supply circuit 3, current i3′ flows in the current-inflow-typeground clamp circuit 4, and current −I flows as the output current Io.

In the conventional ultrasonic transducer drive circuit 1′, in theperiod from time t3 to time t4, as shown in FIG. 11, although thecurrent i2 flows in the negative voltage supply circuit 3, no currentflows in the current-inflow-type ground clamp circuit 4. On the otherhand, in the ultrasonic transducer drive circuit 1, current i3′ flowsalso in the current-inflow-type ground clamp circuit 4, and the outputcurrent Io is split. Consequently, the current i2′ becomes smaller thanthe current i2 (i2′<i2).

When the first transistor Tr1 and the fourth transistor Tr4 enter the onstate at time t6, as shown in FIG. 19, the current i1′ flows in thepositive voltage supply circuit 2, the current i4′ flows in thecurrent-outflow-type ground clamp circuit 5, and the current +I flows asthe output current Io.

In the conventional ultrasonic transducer drive circuit 1′, in theperiod from time t6 to time t7, as shown in FIG. 12, although thecurrent i1 flows in the positive voltage supply circuit 2, no currentflows in the current-outflow-type ground clamp circuit 5. On the otherhand, in the ultrasonic transducer drive circuit 1, the size of theoutput current Io is the same as that in the conventional ultrasonictransducer drive circuit 1′. Consequently, the current i1′ becomessmaller than the current i1 (i1′<i1) only by the amount of the currenti4′ flowing in the current-outflow-type ground clamp circuit 5.

As described above, in the ultrasonic transducer drive circuit 1, duringthe period from time t3 to time t4 and the period from time t6 to timet7, the current flowing in the positive voltage supply circuit 2 and thenegative voltage supply circuit 3 can be reduced as compared with thatin the conventional technique. Thus, the power consumption in thepositive voltage supply circuit 2 and the negative voltage supplycircuit 3 can be suppressed more than that in the conventionaltechnique.

Although the present invention has been described by the foregoingembodiments, obviously, the invention can be modified without changingthe gist of the present invention. For example, each of the ultrasonictransducer drive circuits 1 and 1′ may be provided in the ultrasonicprobe 101.

The invention claimed is:
 1. An ultrasonic transducer drive circuit fordriving an ultrasonic transducer by outputting pulses including apositive pulse and a negative pulse to an output line coupled to theultrasonic transducer, the ultrasonic transducer drive circuitcomprising: a positive voltage supply circuit configured to supplypositive voltage to the output line; a negative voltage supply circuitconfigured to supply negative voltage to the output line; acurrent-inflow-type ground clamp circuit configured to operate whenvoltage in the output line is positive voltage, and configured to changethe voltage in the output line to ground voltage; and acurrent-outflow-type ground clamp circuit configured to operate whenvoltage in the output line is negative voltage, and configured to changethe voltage in the output line to ground voltage, wherein thecurrent-inflow-type ground clamp circuit is configured to enter anoperation state at a time of generating the negative pulse in a statewhere the voltage in the output line is positive voltage; thecurrent-outflow-type ground clamp circuit is configured to enter anoperation state at a time of generating the positive pulse in a statewhere the voltage in the output line is negative voltage; the positivevoltage supply circuit is configured to start operation after a firstpredetermined delay time that lasts from an operation start point of thecurrent-outflow-type ground clamp circuit until the voltage in theoutput line becomes ground voltage; and the negative voltage supplycircuit is configured to start operation after a second predetermineddelay time that lasts from an operation start point of thecurrent-inflow-type ground clamp circuit until the voltage in the outputline becomes ground voltage.
 2. The ultrasonic transducer drive circuitaccording to claim 1, wherein the current-inflow-type ground clampcircuit is configured to operate at least until the positive voltage inthe output line becomes ground voltage, and the current-outflow-typeground clamp circuit is configured to operate at least until thenegative voltage in the output line becomes ground voltage.
 3. Anultrasonic transducer drive circuit for driving an ultrasonic transducerby outputting pulses including a positive pulse and a negative pulse toan output line coupled to the ultrasonic transducer, the ultrasonictransducer drive circuit comprising: a positive voltage supply circuitconfigured to supply positive voltage to the output line; a negativevoltage supply circuit configured to supply negative voltage to theoutput line; a current-inflow-type ground clamp circuit configured tooperate when voltage in the output line is positive voltage, andconfigured to change the voltage in the output line to ground voltage;and a current-outflow-type ground clamp circuit configured to operatewhen voltage in the output line is negative voltage, and configured tochange the voltage in the output line to ground voltage, wherein thecurrent-inflow-type ground clamp circuit is configured to enter anoperation state at a time of generating the negative pulse in a statewhere the voltage in the output line is positive voltage; thecurrent-outflow-type ground clamp circuit is configured to enter anoperation state at a time of generating the positive pulse in a statewhere the voltage in the output line is negative voltage; the positivevoltage supply circuit is configured to start operation after a firstpredetermined delay time that lasts from an operation start point of thecurrent-outflow-type ground clamp circuit until the voltage in theoutput line becomes a voltage in a first predetermined range thatincludes ground voltage; and the negative voltage supply circuit isconfigured to start operation after a second predetermined delay timethat lasts from an operation start point of the current-inflow-typeground clamp circuit until the voltage in the output line becomes avoltage in a second predetermined range that includes ground voltage. 4.An ultrasonic transducer drive circuit for driving an ultrasonictransducer by outputting pulses including a positive pulse and anegative pulse to an output line coupled to the ultrasonic transducer,the ultrasonic transducer drive circuit comprising: a positive voltagesupply circuit configured to supply positive voltage to the output line;a negative voltage supply circuit configured to supply negative voltageto the output line; a current-inflow-type ground clamp circuitconfigured to operate when voltage in the output line is positivevoltage, and configured to change the voltage in the output line toground voltage; and a current-outflow-type ground clamp circuitconfigured to operate when voltage in the output line is negativevoltage, and configured to change the voltage in the output line toground voltage, wherein the positive voltage supply circuit isconfigured to start operation at the same time as the operation start ofthe current-outflow-type ground clamp circuit; and the negative voltagesupply circuit is configured to start operation at the same time as theoperation start of the current-inflow-type ground clamp circuit.
 5. Theultrasonic transducer drive circuit according to claim 1, wherein thepositive voltage supply circuit includes a first transistor configuredto start and stop supply of the positive voltage to the output line. 6.The ultrasonic transducer drive circuit according to claim 5, whereinthe operation start timing of the current-inflow-type ground clampcircuit is a timing when the first transistor changes from an on stateto an off state.
 7. The ultrasonic transducer drive circuit according toclaim 5, further comprising a first driver circuit configured to drivethe first transistor.
 8. The ultrasonic transducer drive circuitaccording to claim 1, wherein the negative voltage supply circuitincludes a second transistor configured to start and stop supply ofnegative voltage to the output line.
 9. The ultrasonic transducer drivecircuit according to claim 8, wherein the operation start timing of thecurrent-outflow-type ground clamp circuit is a timing when the secondtransistor changes from an on state to an off state.
 10. The ultrasonictransducer drive circuit according to claim 8, further comprising asecond driver circuit configured to drive the second transistor.
 11. Theultrasonic transducer drive circuit according to claim 1, wherein thecurrent-inflow-type ground clamp circuit includes a third transistorconnected between the output line and the ground such that when thethird transistor is in an on state, current flows in from the outputline.
 12. The ultrasonic transducer drive circuit according to claim 11,further comprising a third driver circuit configured to drive the thirdtransistor.
 13. The ultrasonic transducer drive circuit according toclaim 1, wherein the current-outflow-type ground clamp circuit includesa fourth transistor connected between the output line and the groundsuch that when the fourth transistor is in an on state, current ispassed to the output line.
 14. The ultrasonic transducer drive circuitaccording to claim 13, further comprising a fourth driver circuitconfigured to drive the fourth transistor.
 15. The ultrasonic transducerdrive circuit according to claim 1, wherein the pulses are voltagepulses.